medium voltage protection guide

As the power requirements increase, so too does the likelihood that the utility will require a higher service voltage. The majority of modern relays are multifunction type with the protection referred to by numbers that correlate with the functions they perform. Industry standard protection schemes for the transformer secondary include a circuit breaker equipped with long-time, short-time, instantaneous, and ground fault functions. CTs interface the electronic device and the MV primary system. This form of protection employs relays with inverse time-current characteristics; that is, operating time of these relays becomes less as the current magnitude increases. Each product is backed by an efficient worldwide distribution network with unrivaled service and technical support. In some cases a protection relay is used with the aim of activating automatisms to manage the electric network. Bussmann is a world-leading supplier of medium voltage fuses. Protective devices are redundant—no matter which device opens, the same outage occurs. Learn about power engineering and HV/MV/LV substations. To be clear, a properly sized and rated transformer includes the following features: The 2011 NEC requires that transformers be protected against overcurrent (NEC Article 450.3). When voltage is switched on to energize a transformer, the transformer core normally saturates, which results in a large inrush current. The utility will include required setting parameters and limitations based on the manufacturer for the protective devices. Medium-voltage surge arresters Surge arresters are used for protection of electrical equipment from all kind of overvoltages caused by lightening or switching operations. 7.6 Protection of Low-Voltage Capacitors. However, unless precautions are taken, this setting may be too low to prevent relay misoperation on inrush following an outage. This paper covers general safe operations on Medium Voltage equipment and looks at the aspects of Switching, Isolating, Testing and Earthing, as well “E” fuse ratings should always be greater than the transformer full load amps (FLA). Short-circuit protection is still required. Learn about code and standard “minimums” that must be considered in the coordination of MV protective devices. Settings do not correspond to those listed as standard in the NEC [NEC Article 240-6(a)]. Although the primary windings are rated for MV, the designer must choose either fuses or circuit breakers to protect the transformer. For balanced distribution systems, the ground relay can be set to pick up as little as 25% of load current. Adequate capacity for the load to be served, Adequate temporary overload capacity (kVA size, or ratings), Primary and secondary voltages properly rated for the electrical distribution system. In this case an analysis of options must be conducted to determine the best option for the project. The protective relay curve only represents the action of a calibrated relay and does not account for the actions of the associated circuit breaker or the accuracy of the current transformers that connect the relay to the monitored circuit. The norm, however, is that the utility will give several MV services that the engineer will need to integrate into an owner’s MV distribution system. ABB Surge Arresters — Buyer’s Guide Edition 5, 2003-10 1 High Voltage Surge Arresters Buyer´s Guide. NEC Article 490 covers equipment, over 600 V nominal. To accomplish this, the fuse curve should be to the right of the transformer inrush point and to the left of the cable damage curve. NEC Articles 215.10, 230-95, and 240.13 require ground-fault protection for solidly grounded wye systems of more than 150 V to ground circuits, which includes 277/480 V “wye” connected systems. ANYWHERE DURABILITY. 15 • Outdoor medium voltage padmounted switchgear - … It will help you. Magnetizing inrush currents to transformers. Auxiliary power is used only for communication and high sensitivity earth fault protection. Medium voltage fuses are applied quite differently than fuses rated 600 volts and less. The motors in our new product series are thus all placed in the medium voltage category,” says Bjarne Nør. NEC 310.60(C) and Tables 310.77 through 310 list ampacity of MV conductors 2001 to 35000 V. NEC Art 210.9(B) (1) requires the ampacity of the branch circuit conductors shall not be less than 125% of the design potential load. To see the list of application documents for the product, go to the Specifiers Guide. However, in the past 15 years, there has been an explosion of MV electrical distribution systems used in large commercial complexes. IEC – 61800-5 AC Drives Standard 6. The medium voltage quality system has been certified as being fully compliant with the requirements of the ISO 9001:2015 quality assurance model. System Backup Protection (51V, 21) • For medium and small sized generators, voltage-restrained or voltage controlled time overcurrent relays (51V) are often applied • Control or restraining function used to prevent or desensitize the overcurrent relay from tripping until the generator voltage is reduced by a fault Protection of a power system depends on its architecture and the operating mode. The rated secondary current is commonly 5 amp, though lower currents such as or 1 amp are not uncommon. Safety requirements ensure equipment is of sufficient rating to withstand the maximum available energy of the worst-case scenario. For emergency and legally required standby feeders, NEC Articles 700.26 and 701.26 require the ground fault device shall be an alarm only. Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of industrial process and its service continuity requirements, with the status of the neutral, characteristics of the machines, levels and duration of the fault currents, etc. He has more than 28 years of engineering and design and field experience that includes MV distribution systems for military, mining, tunneling, food manufacturing, power production facilities, high-rise facilities, and casino resort complexes. Medium- Voltage Switching Devices and Switchgear. To coordinate an overcurrent relay with other protective devices, a minimum time margin must be incorporated between the curves. This is why type 3EK medium-voltage arresters for distribution networks can be equipped with an Arc Protection System (APS), which is installed at both ends of the surge arrester. NEC Article 493.30 lists the requirement of metal-enclosed switchgear. Unlike low-voltage breakers and fuses, MV circuit breakers do not have fixed trip. 3. The ground conductor is required to be sized per Table 205.122. Device 50 or instantaneous: Set below cable damage curve and must be above the maximum fault current at the breaker total clear curve. Device 51 or function long-time pick-up (LTPU): Recommend 100% to 125% of the transformer FLA and set below the transformer and cable damage curves. Feeder and transformer protection is defined by the applicable equipment standards. Equipment protection: Protection requirements are met if overcurrent devices are set above load operation levels and below equipment damage curves. An excessive number of protections may also be harmful, since, even if they operate correctly in the case of a fault, they can operate, Get access to premium HV/MV/LV technical articles, advanced electrical engineering guides, papers, and much more! Article 700.27: Emergency Systems Coordination, iii. Bussmann circuit protection solutions comply with major international standards: ANSI, BS, DIN, IEC and UL. Typically, service reliability tends to increase as service voltages increase. Most solidly grounded MV distribution system short circuit currents can be well above 10,000 amps. For this article, a good working definition of MV is 1 to 38 kVac as any voltage level above 38 kV is a transmission level voltage versus a distribution level voltage. Under a fault condition, the fault current can easily exceed the capacity of the cable tape shield or concentric neutral ground; hence, a separate ground wire is necessary. United States Department of Agriculture Rural Utilities Service RUS Bulletin 1724E-300 Issued June 2001 Design Guide for Rural Substations Medium voltage switchboard system from 1 to 36 kV Sepam Protection relays Masterpact Protection switchgear from 100 to 6300 A A consistent design of offers from Medium Voltage to Low Voltage Guiding tools for more efficient design and implementation of your installations The Guide Design office, consultant, contractor, Medium Voltage One Line Click here to switch to Low Voltage One Line Medium Voltage Distribution VIP Selection guide 01 (1) The protection is self-powered. Understand overcurrent protection requirements for medium-voltage distribution transformers. In some cases, the utility may provide options for the service voltage. Typically, the fuse will cross the transformer damage curve in the long time region (overcurrent region). In distribution design, the three objectives still apply: For example, if the NEC requirements for transformer overcurrent protection are considered without reference to applicable standards and code requirements, the system may address protection of transformers, while other elements of the distribution system (such as the feeders connecting the transformer(s) to the distribution system) may not be protected in accordance with the code. Long-time delay (LTD), STPU, and short-time delay (STD): Set to coordinate with downstream devices and below the transformer damage curve. Guide Form Specification RC-Snubber for Transformer Protection 1 General 1.1 This specification is for a _____ kV (line-line voltage) medium voltage three phase metal-enclosed RC-Snubber. The latter is a special application although normal in plants, but in this case the relays cannot be considered as network and plant protections. For the purpose of this guide, transformers having primary voltage ratings between 34.5 kV and 138 kV, with medium-voltage (4.16 kV through 34.5 kV) secondaries, will be covered. Motor and generator curves are machine specific and are normally provided in the vendor data submittal packages. In addition, the engineer must ensure that the setting does not exceed the maximum available fault current or the instantaneous trip will be rendered worthless. Such overcurrent protection does not necessarily protect the primary or secondary conductors, or the equipment connected on the secondary side of the transformer. For transformers greater than 5 MVA, protection schemes become more complex. Additionally, the ground fault protection shall be selectively coordinated per NEC Article 517.17(C). Our proprietary material formulations offer anywhere durability – even in HV-polluted environments. Increasing this setting may restrict feeder coverage or prevent a reasonable setting of upstream or source side fuses and protective relays. Another feature of large commercial complexes is the associated central plant function with MV chillers and unit substations. Distribution voltages are typically medium voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the local utility. Search Products And Discover New Innovations In Your Industry, i. However, for large-scale developments, equipment such as large motors may require a service voltage of 4160 V or higher. Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of indus-trial process and its service continuity requirements, with the status of the neutral, characteristics of the machines, levels and duration of the fault currents, etc. The current will go to a high value when a fault occurs. Selectivity comprises two major categories: a. Transformer MV breakers may include the following protective device numbers: In MV systems, current transformers (CTs) connect protective or metering devices. It is important to underline at once that trip selectivity must always be looked for, but must only be looked for after having ensured protection of the network component. When connecting to an existing utility, the utility typically directs the interconnection requirements including protective device requirements. Hitachi ABB Power Grids has more than 100 years of experience in designing and manufacturing surge arresters and protection devices. 2. Medium-voltage dry type transformers. The input for a distribution substation is typically at least two transmission or subtransmission lines. 147. NEC Section II (Article 300.31 through 300.50) covers MV wiring methods. The installation on neutral grounding resistor should be considered to limit ground fault currents to a safe level for MV generation systems. To improve overall system protection and coordination, redundant devices are intentionally set to overlap (i.e., non-selectivity coordinate with one another). Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of indus-trial process and its service continuity requirements, with the status of the neutral, characteristics of the machines, levels and duration of the fault currents, etc. Passive fire protection, fire resistant cable, hydrocarbon fire ... IEC 61892-4 does not provide a cable selection guide other than for a simple CF scenario. This is especially true for delta primary and wye secondary, where a secondary ground fault may not trip the primary protection. Voltages 600 V and below are referred to as “low voltage,” voltages of 600 V to 69 kV are referred to as “medium voltage,” voltages of 69 kV to 230 kV are referred to as “high voltage,” and voltages 230 kV to 1,100 kV are referred to as “extra high voltage” with 1,100 kV … Complete guide to protection of machines and plants in medium voltage networks (photo credit: ABB) Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of industrial process and its service continuity requirements, with … In cases involving redundant protective devices, nonselective breaker operation is of little or no concern. Sizing MV components such as motors, generators, transformers, wiring systems, the architecture of MV systems, or design of complicated protection schemes such as reclosers, zone interlocks, differential protection, etc., are all beyond the scope of this article. 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What you 're thinking... we care about Your opinion NEC Section ii ( 300.31! Require the ground relay can be set to pick up as little as 25 % of the load.: E-rated power fuses are not reflected in the vendor data submittal packages way as circuit! The protective function numbers that are more complicated, a minimum time margin must be the. 1501 to 7200V AC ICS ( formerly ICS2-324 ) 5 and can not be required to small! Circuit breaker equipped with long-time, short-time, instantaneous, and ground fault device be. Numbers are based on globally recognized IEEE standards as defined in IEEE standard C37.2 problem is the of... Highest possible service continuity to avoid damage to network components resistor should be at...
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